In-growth Of The 59.54 Kev γ-ray Line In Freshly Stripped Samples Of Plutonium

At about 14.3 years, 241 Pu has the shortest half-life of the abundant plutonium isotopes present in the products of reprocessed irradiated nuclear fuel. This short decay time of 241 Pu is largely responsible for the changing isotopic distribution of plutonium samples. The predominant decay mode of 241 Pu is via β-emission to 241 Am, which in turn α-decays to 237 Np with the emission of a characteristic 60 keV photon. The minority decay channel is through α-emission to 237 U, which in turn β-decays also to 237 Np, with the emission of the same 60 keV transition. Detection of the 60 keV photon is a way to identify and quantify low levels of 241 Am in plutonium-contaminated materials. To fairly assess minimum detection limits of 241 Am as a function of starting conditions and sample age, understanding the temporal behavior of the 60 keV intensity is necessary. In this note, we discuss the relative contributions to the 60 keV emission rate from the two branches and how the combined intensity evolves over time.